Process of cutting polyamide filaments



y R. L. KEEFE, JR 2,887,155

- PROCESS OF CUTTING POLYAMIDE FILAMENTS Filed June 28, 1955 "Fig.1

' Fig 2 6 3b |2 H I30 v -30 14 T Fig.3

INVENTOR ROBERT L. KEEFE-,JR.

l v BY I4- NQm ATTORNEY United Sttes Patent PROCESS OF CUTTING POLYAMIDE FILAMENTS Robert L. Keefe, Jr., Collins Park, Del., assignor to E. I. du Pont de Nemours and Company, Wilmington, DeL, a corporation of Delaware Application June 28, 1955, Serial No. 518,494

4 Claims. (Cl. 164-17) This invention relates to manufacturing of staple fibers from continuous filaments.

Processing of fiber-forming polymeric compositions into filamentary form is well known, the initial self-supporting structure customarily being agroup of continuous ized by exceptional tensile strength and physical toughness, especially when drawing or a similar step has induced macromolecular orientation along the filamentary axis. Orientation may be accomplished at any time after the product is extruded or spun into solid filamentary form, and French Patent 976,505 to Bata teaches a convenient method of producing tenacious nylon filaments by rapid extrusion and windup without necessity for a subsequent conventional drawing step. staple fibers from continuous filaments produced at speeds on the order of several thousands of yards per minute necessitates very rapid cutting or equivalent division of the product into relatively short lengths, as is usually accomplished by known types of mechanism operating by impact against the side of the filaments; however, the polyamidesand particularly polycaproamide-have not cut satisfactorily at high speeds, the extreme difiiculty for polycaproamide being attributed in part to .plasticization owing to residual monomer content.

A primary object of the present invention is improved production of polyamide staple fibers. A particular object is high-speed cutting of a bundle of polycaproamide filaments into separate staple lengths with minimum dulling of the cutter blade. Other objects of this invention, together with means and methods for attaining the various objects, will be apparent from the following description and the accompanying diagrams.

Figure 1 is a schematic cross-sectional representation of apparatus useful in carrying out this invention. Figure 2 is a similar representation omitting a part of the apparatus of Figure 1. Figure 3 represents an alternative form of a group of elements of the apparatus of Figure 1. Figure 4 represents an alternative construction of the topmost elements of Figure 1.

In general, the objects of the present invention are accomplished by exposing tenacious polyamide filaments to superheated water vapor and immediately forwarding them to mechanism for cutting. The invention comprehends particularly reheating of tenacious as-spun polycaproaniide filaments to' a temperature of from about 110 C. to about 200 C. in the presence of an amount of water vapor on the order of hundredths of a pound per pound of dry air for a time on the order of hundredths of a second and immediately cutting the filaments into staple lengths. Use of hot moist air to forward the filaments to the cutter is a preferred method of operating according to this invention, which is exemplified below in some detail.

Figure 1 shows bundle of filaments 1 traveling ver- Production of i tically downward among elements of apparatus represented in cross section. The filaments enter the flared opening of aspirating jet 6 whose outlet joins the top end of cylindrical conduit 2 through which the filaments pass to exit just below the bottom of surrounding jacket 4. The jacket has side opening 3a at the top and 3b at the bottom to accommodate electrical leads 13a and 13b to heating element 7, which is in the form of a resistance tape wrapped helically around the conduit. The jacket has near the top a side opening closed by supply tube 5 opening into the jet. Below the exit end of the conduit at the bottom of the jacket is aspirating jet 8 with side tube 9 for air input and short vertical exit tube 10 through which the filament bundle passes to be intercepted by blade 11 of arm 12 of a flying knife type of impact cutter. Below the intersecting location, discontinuous filamentary lengths 21 are visible inside short conduit 14, which leads to condenser 15 having suction tube 16 connecting therewith near the bottom below the location of perforated screen 17 upon which pile 18, of cut staple accumulates.

Operation of the illustrated apparatus is readily understood. Hot moist air enters the upper aspirating jet through the side tube and passes downward through the conduit to exhaust at the bottom. The flow of air pulls the filaments down through the conduit, and upon exiting therefrom they are forwarded out the bottom tube of the lower aspirating jet by air flow into its side tube. At frequent time intervals the knife passes horizontally just beneath the exit of the lower jet and above the underlying short conduit and cuts the filaments into staple lengths. The cut staple falls through the conduit underneath onto the collection screen. The heating tape is maintained at a suitable temperature, usually some what above that of the hot moist air, to prevent condensation of water and to ensure satisfactory treating temperature throughout the main conduit.

By way of example, flake polycaproamide with a relative viscosity of 41 (measured as in Patent 2,385,890) and containing 0.2% titanium dioxide by weight is melted, filtered, and extruded in conventional manner through a ZOO-orifice spinneret into air at room temperature. The filaments, which cool and solidify in the air, are converged 54 inches below at the entrance of an upper aspirating jet of apparatus like that described above. Forwarded by this jet the filaments increase permanently in length somewhere between the face of the spinneret and the entrance to the jet, at which point no further decrease below 3 deniers per filament is apparent. The jet is supplied with air at 170 C. containing 0.0175 pound water per pound of dry air at a rate effective to forward the filament bundle through the conduit, which is stainless steel with inside diameter of V1. inch and length of 4 /2 feet, at a rate of 3500 yards per minute. The electrical potential supplied to the heating tape is adjusted to maintain a temperature of 200 C. at the inside wall of the conduit. The filament bundle is for-. warded immediately from the exit of the conduit by a jet like the lower jet of the illustration, operated with air at room temperature, to a flying-knife cutter, which cuts the filaments into 2-inch lengths at a repetition frequency of slightly over 60,000 cuts per minute. The cut staple is collected in a conventional condenser, pounds having relative viscosity of 37 and 8% waterextractable content being collected in a continuous operating period of 3 /2 hours.

An attempt to operate the above apparatus by air similarly heated but containing only 0.004 pound Water vapor per pound of dry air jammed the cutter with tacky uncut filaments in less than a minute. Operation with the heating tape inactivated and with saturated steam at atmospheric pressure drawn into the supply tube as the yarn is forwarded by the lower jet did not affect the cutter directly, but the cut lengths stuck together, and the exit from the cutter became clogged with staple.

Operation upon filaments of polyhexamethylene adipamide (relative viscosity of 63 and 0.3% content of titanium dioxide delusterant) proceeded satisfactorily with forwarding air at the moisture level of the example but heated to 180 C. with the conduit heated to 210 C. by the resistance tape; substitution of air at room temperature for the hot moist air to the jet jammed the cutter in less than a minute of operation.

As shown in Figure 2, the lower operating jet may be omitted; in this modification the filament bundle meets the cutter immediately upon exiting from the bottom of the main conduit. For some deniers it may be desirable to retain a lower jet and even to eliminate the space between it and the main conduit; thus, as in Figure 3, lower jet 8 with side tube 9 may be consolidated at the top with the bottom wall of the jacket to receive extended exit end of main conduit 2' at the entrance of the jet, with the cutter located close to the exit tube of the jet. Furthermore, when this integral arrangement is employed for the lower jet, the upper jet may be eliminated, as in Figure 4; however, there string-up will be facilitated by introduction of side tube 19 slanting downward into main conduit 2" and supplied with stop-cock 20 to permit temporary injection of added air, air being drawn into the top of the tube continuously through side tube of jacket 4 modified to receive it. In these diagrams the reference characters of Figure 1 are applied unchanged throughout to the original elements, and altered elements are designated by corresponding primed numbers. Of course, other relatively minor apparatus modifications may be utilized with satisfactory results. As the filaments are converged at the entrance to the apparatus, if not beforehand, the top of the apparatus should not be closer to the spinning (i.e., extrusion) zone than the minimum quench distance for the filaments, usually one to two yards or so.

When both top and bottom jets are used, at least the top jet will be supplied with the hot moist air; the lower jet also may operate with hot moist air, but that usually will be unnecessary. Of course, when only a lower jet is used, the entrance at the top of the main conduit must open into an atmosphere of suitable temperature and humidity, as the jet will draw air from there through the conduit; consequently, a larger diameter of conduit is desirable with this arrangement than when an upper jet is present. Moisture content of from about 0.01 to 0.10 pound of water vapor per pound of dry air is desirable in any event.

The yarn-reheating conduit 2 may be from about one and one-half to about five and one-half feet long or longer. Longer lengths (over 5 /2 feet) increase the back pressure on the yarn-aspirating jet and require an excessive height for the spinning machine without any compensating advantage. Shorter tubes than 1% feet generally give the yarn insufiicient time in which to attain the required temperature. A tube of 3 to 4 /2 feet in length is usually preferred. The relation of conduit length to speed of filament passage usually should be such as to keep the filaments in the conduit for a time not less than half a hundredth nor more than several hundredths of a second.

The upper limit of temperature of the main conduit is set by the softening or sticking temperature of the filaments being processed, and 200 C. is a good operating limit for most compositions; the lower limit of temperature is established by difiiculty in cutting, which usually increases toward and below the lower end of the recommended range. The upper limit of moisture is imposed by adhesion of the fibers to one another almost as if fused, and the lower limit is provided by considerations like those for the lower temperature limit. Usually slight excess of temperature of the conduit itself over that of the moist air will permit operation at a higher moisture level than otherwise practicable. At satisfactory levels of moisture in the lower part of the recommended range separate heating of the conduit may be eliminated if desired. Furthermore, in some instances the water vapor may be supplied in part by the filaments themselves, especially when their initial moisture content exceeds 0.2% by weight; such content is not customary in fiber-forming polymers, however, because prolonged exposure of such polymer to melting temperature will be accompanied by hydrolysis to decreased viscosity.

If desired, the water vapor may be replaced or supplemented by other hydroxylated non-solvents for nylon;

examples of suitable non-solvents, notably alcohols, are disclosed by Miles in Patent 2,289,377. The well-known commercial nylon polymers mentioned above are only illustrative, as the invention extends generally to treatment of polyamides formed from amino-carboxylic acids or their lactams or from diamines and dicarboxylic acids or their amide-forming derivatives. The polymers may contain pigments and delusterants, as exemplified above by titanium dioxide, or antioxidants, dyeing assistants, and the like without affecting operations adversely. The action of any suitable cutter will be improved by the practice of this invention.

The claimed invention:

1. Process comprising exposing tenacious polyamide filaments to hot moist air containing from about 0.1 to about 0.01 pound water vapor per pound of dry air at a temperature between about C. and about 200 C. for a time of about at least 0005 second and immediately thereafter cutting the filaments.

2. The process improvement of claim 1 in which the polyamide of which the filaments are composed is polycaproamide.

3. Process comprising forwarding tenacious as-spun References Cited in the file of this patent UNITED STATES PATENTS 2,130,948 Garothers Sept. 20, 1938 2,157,117 Miles May 9, 1939 2,287,099 Hardy et al June 23, 1942. 2,327,460 Rugeley Aug. 24, 1943 2,341,823 Smith Feb. 15, 1944 2,733,122 Herele et al. Jan. 31,1956 

1. PROCESS COMPRISING EXPOSING TENCIOUS POLYAMIDE FILAMENTS TO HOT MOIST AIR CONTAINING FROM ABOUT 0.1 TO ABOUT 0.01 POUND WATER VAPOR PER POUND OF DRY AIR AT A TEMPERATURE BETWEEN ABOUT 110* C. AND ABOUT 200* C. FOR A TIME OF ABOUT AT LEAST 0.005 SECOND AND IMMEDIATELY THEREAFTER CUTTING THE FILAMENTS. 